import std.algorithm, std.array, std.container, std.range;
import std.string, std.conv;
import std.math, std.bigint, std.bitmanip, std.random;
import std.stdio, std.typecons;

void main()
{
  auto n = readln.chomp.to!int;
  auto ai = readln.split.map!(to!int).array;

  auto r = iota(n - 2).count!(i => isKadomatsu(ai[i..i + 3]));
  writeln(r);
}

bool isKadomatsu(int[] ai)
{
  return (ai[0] != ai[1] && ai[0] != ai[2] && ai[1] != ai[2]) &&
    ((ai[1] < ai[0] && ai[1] < ai[2]) || (ai[1] > ai[0] && ai[1] > ai[2]));
}